Providing useful traits that cannot be provided by cross breeding to a plant by introducing foreign genes to plant cells is extremely meaningful in future improvement of crops and development of agriculture. Furthermore, in order to establish a substance production method by plants using carbon dioxide as a raw material, as a novel substance production method alternating a petroleum-dependent substance production method, it is indispensable to use a plant genetic recombination technique.
As a method of introducing a gene into a plant cell, an Agrobacterium method using infection with a soil bacterium, i.e., Agrobacterium, a particle-gun method and a viral vector method are known. The Agrobacterium method is the most frequently used in introducing a gene into a plant cell. However, there are many economically important plants to which a gene cannot be introduced by the Agrobacterium method, at present. The particle-gun method has been much more generally used compared to the Agrobacterium method; however, device cost is high. In addition to this problem, there is a risk of damaging a gene and transformation efficiency is low. The viral vector method is advantageous compared to the Agrobacterium method since transformation efficiency and gene expression efficiency are high; however, the method has a problem in that the size of the gene to be introduced is limited and viral infectious ability is low. In the circumstances, it has been desired to develop a novel method of introducing a gene, which is simple and widely applicable to all types of plants and genes.
It is known that a cell-penetrating peptide (CPP) has a function of transporting a complex comprising the peptide and another substance (for example, a protein and a nucleic acid) through biomembrane of mammalian and human cell strains. However, use of CPP in plant cells is limited. Unlike animal cells, plant cells have double barriers, i.e., cell wall and cell membrane, for preventing internalization of a complex comprising CPP. In the meantime, it is disclosed that a polycationic peptide concentrates negatively charged DNA by ionic interaction to form a complex that can be used for gene delivery, and that such a complex is useful for introducing a gene into animal cells (Patent Document 1: WO2011/006133). It has been also reported that a polycationic peptide was used for introducing a gene into a plant protoplast (Patent Document 2: JP Patent Publication (Kokai) No. 7-213285). However, the method employs a protoplast without a cell wall. In addition, it cannot be said that gene introduction efficiency into a plant cell is sufficient, in this method.